This invention relates to a controller for a battery-powered forklift car and so on, and particularly to an electric-car controller suitable for controlling a by-pass contactor.
An example of an electric-car controller is disclosed in JP-A-61-106006. In this example, when an acceleration command reaches a certain specified value or above and the chopper duty factor becomes more than a specified value, or when the acceleration command is maintained at a certain value or above for a predetermined time, the by-pass contactor is turned on. However, when the load on the car is large or when the car starts to go up a slope, the chopper duty factor is not increased because of the current limiting action of the chopper. Since the by-pass contactor is turned on after a constant delay and then the car is accelerated, the acceleration occurs in two steps, thus producing an unpleasant sense of acceleration. Moreover, since a current close to the current limit value (maximum control current) flows in the chopper during the predetermined delay, the chopper element generates a lot of heat. The original object of the by-pass contactor is to produce a driving force greater than that produced by the chopper by directly applying a DC source voltage to the DC motor. Thus, it is necessary to turn on the by-pass contactor faster for a larger running load such as when the car starts to go up a slope or when the load on car is large. The conventional apparatus, however, does not consider this aspect, and thus the by-pass contactor is turned on later for a large running load than for a small running load.